Polymer products and process for producing the same



R. C. HOUTZ July 23, 1946.

POLYMER PRODUCTS AND PROCESS FOR PRODUCING THE SAME Filed NOV. 4, 1944 uk7 L swwwwwwwwwwwwwwwwwwwww.

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I ATTORNE Patented July 23, 1946 a 2,404,721 QPOLYMER PRODUCTS atPEODUCING l 9 Clyde,Houtzf,,Snyder, N. Y; ,"a"ssi'gn6r-to E. du Pont dcNemoui-s 8: Company; Wilmington Del.,a corporatlon of Delaware;Application November 4, last: a ,jniol unsi (01. 260-32) This inventionrelatesito anew composition of matter and shapedarticles-producedtherefrom. More particularly, this invention relates toan organic solvent solution of polyacrylonitrlle, i. .e. polymerizedacrylonitrile wor polymerized vinyl cyanide (CH2=CHCN) 1, ,andcopolymers; and interpolymers of acrylonitrile inwhich atgleast 85% byweight of the polymer is acrylonitrile, and to the production of shapedarticles from saidorganic solvent solution of said polymersof acrylo-jnitrile.

This application is a continuationin part of the copending applicationofRayClyde 'Houtz,

Serial No. 447,446, filed June 17,1942. t

Polyacrylonitrile, and copolymers and inter polymers of acrylonitrilewith otherr tpolymerizable substances, for examplevinyloracryliccompounds, in which at least 85% by weight of the polymer isacrylonitrile havebeen known ,for some time and recognized aspossessingdesirable physical and chemical properties including toughnessand insolubility in and insensitivity to common organic solvents such.as methyl or ethyl alcohol, acetone, ethylether, ethyl acetate, hy-

drocarbon solvents, chlorinated hydrocarbons and the like. Becauseof-these facts numerous attempts have been made to form these polymericmaterials into yarns, films and other shaped articles. he

s s The copending application oi =qeorgef Latham, Serial No. 562,012,filedoimevennat e herewith discloses solutions of polyacrylonitrile indimethyl carbamyl compoundsandthe. production of extruded and otherwiseshaped articles and structures from such solutions. 1 The abovesaidapplication of George H. Lathaln represents the first successfuldissolutionof.polyacrylonitrile in a solvent to produce a solution whichisfsuitable for the production oi commerciallyluseful textile yarns orwrapping tissue films and similar tough, flexible structures.

The present application relaltesrtoasimilarly satisfactory dissolutionof, polyacrylonitril iin an organic solvent taken fror n'ja differentclassof organic compounds and the polyacrylonitrile solutions producedthereby aref v jmilarly satisfactory for the production of'tough,fiexible,,dense, color less yarns and films which aresuitable ior use inpractically all general commercials applicw tionsof suchproducts, W k Ithas been known heretofore thflticonc trated aqueous solutions ofinorganic salts sucl' fas lithium bromide, zinc chloride andsodiu'm"suIfQcIy-j anide will dissolve polyacryl onitrile and fitj has beenproposed (minors. I'a intNo. '2,1f4'0;92 l) without breaking.

ass Fort substantially impossible'f t positions in such a mannercoagulating bathsf of the mg suchnon solvents To the fonnation 'df shapeart large amounts of theuiorga -a d the structure possesses.poor?physicalipropertlesfi -I moyal or ;.these. salts;;;,when; :spos'slble;result in theiformation'lof aporous'; spongy; weak, undesir ablstructure ithatl :is we 2 brittle-1 and 1 completely unsuitedzaforuseless at omfilmi. Moreover; when ittisvattemptedltoIormaamultifilament-yam bypextruding. :ior exampleiithezrproposed aaqueous sodium sulfocyanlde polyacryloriitrileZ'coxnposis tion, into ai1ute\acid=lb.ath;-i spfound thatsthe individual @filamentsiyohtainetick" togetheiwzpto o mianess v vi y mpnefila e t t is"extremelytbrittle and cann q Ynewe1 insp9l acrylonitrile' containinghi'gli'e acrylonitrile i e. acrylonitril mentary structures such asyarns from the composition. Films or fllamentswhen obtainable, areextremely brittle; they are highly colored and very weak, presumablybecause of the presence within them of residual quaternary ammoniumsalt. Removal of this salt is difllcult and'the which does not reactwith or decompose the polymer and which may be substantially completelyremoved from the structures formed of such a solution.

It is another object of this invention to produce a solution ofpolyacrylonitrile or a copolymer or interpolymer of acrylonitrile inwhich at least 85% by weight of the polymer is acrylonitrile, in asolvent which does not react with or decompose the polymer, the solutionbeing suitable for the formation of commercially useful, void freearticles of polyacrylonitrile, for example yarns which are suitable astextile yarns and films which are suitable as wrapping tissue.

It is another object of this invention to produce a solution ofpolyacrylonitrile, or a copolymer or interpolymer. of acrylonitrile inwhich at least 85% by weight of the polymer is acrylonitrile, in avolatile organic solvent, which solution is stable over extended periodsof time and is eminently suited for use in the manufacture of shapedarticles such as yarns, films, tubes, straws. artificial horsehair,bristles and ribbons, or when highly concentrated, for use in themanufacture of molded articles.

It is a still further object of this invention to produceshaped articlesand structures of polyacrylonitrile, or copolymers or interpolymers ofacrylonitrile in which at least 85% by weight of the polymer isacrylonitrile.

It is still another object of this invention to produce a shaped articleor structure of polyacrylonitrile or copolymers or interpolymers oiacrylonitrile in which at least 85% by weight of the I polymer isacrylonitrile, for example a yam, film, tube, bristle or the like whichis tough, flexible, tenacious and free from voids.

Other objects of the invention will appear hereinafter. I

The objects of the invention may be accomplished in general bydissolving polyacrylonitrile, or copolymers or interpolymers ofacrylonitrile in which at least 85% by weight of the polymer isacrylonitrile, in an aromatic compound which is not a salt and whichcontains at least one hydroxyl group and one nitro group attached to thesame ring, the valcnces of the ring members being otherwise satisfied byhydrogen atoms.

If the solvent has a relatively low boiling point (less than about 250C.), the solution of acrylonitrile polymer may then be formed into ashaped structure, for example a yarn or film, and the solvent removedfrom the shaped structure. When the solvent is relatively non-volatileand has a I the above-mentioned acrylonitrile polymers includem-Nitrophenol p-Nitrophenol l-nitro-beta-naphthol 3-nitro-beta-naphtholi4-nitro-beta-naphthol Z-nitrQ-alpha-naphthol 3-nitro-alpha-naphthol4-nitro-alpha-naphthol acrylonitrile polymer solutions formed by the useof the solvents described above are stable at room temperature(approximately 20 C.) and at temperatures considerably above roomtemperature. Shaped structures and articles can be produced by extrudingsuch solutions into an evaporative or coagulative medium. By forming thestructures in an evaporative medium, the solvent must be evaporatedtherefrom and by forming the structures in a coagulative medium, thesolvent should be removed by selective solution in a non-solvent for thepolymer.

The solutions are prepared by dissolving the polyacrylonltrile, orcopolymer or interpolymer of acrylonitrile with one or a mixture of theabovementioned solvents. Some of these solvents are solid at ordinarytemperatures and dissolve or retain the polymer in clear solution onlyat elevated temperature, for example at temperatures of 100 C. orhigher, below which temperature the composition resembles a gel. In allcases when the polymer or copolymer is dissolved in a solvent of theabove class, the resulting composition, while hot, has the appearance ofa true solution. When cooled to room temperature, the compositiongenerally takes on the appearance of a gel, which gel may, on prolongedstanding, undergo syneresis. Reheating of this gel or syneresed masshowever causes it to again return to solution form. I

In view of the relatively high melting points of some of the solvents ofthis invention, they would have comparatively little use in theproduction of a polyacrylonitrile spinning or casting solution. Suchsolvents are however excellent solvent plasticizers forpolyacrylonitrile since they are soluble in a. wide range of proportionswith the said acrylonitrile polymers. The present invention thereforecontemplates solid solutions of acrylonitrile polymers containing atleast by weight of acrylonitrile as well as liquid solutions thereof. I

Shaped articles obtained from solvent solutions of polyacrylonitrile inaccordance with the invention and from which the solvent is subsequentlyremoved are substantially free of foreign matter and voids andsubstantially undecomposed and I chemically unchanged from the polymerprior to its solution.

The above-described organic solvent solutions of acrylonitrile polymermay be shaped in the form of filaments, yarns, films, tubes and likestructures by apparatus and processes generally known in th art, thedetailed operating conditions being suitably modified.

Suitable methods and apparatus for the production of shaped articles ofthe polymers of this invention will be readily apparent by reference tothe following detailed descriptionwhen taken in connection with theaccompanying illustrations in which:

Figure 1 is a diagrammatic vertical sectional view showing a dryspinning cell suitable for use in accordance with the invention;

in accordance with the invention.

- Referring to Figure l of the drawing, reference numeral I l designatesa spinneret through which a plurality oi filaments II are formed byextruding a filament-forming solution supplied to the spinneret by meansof conduit I 3. The spinning cell is jacketed with a material I 1 suchas a refractory in which is embedded an electrical heating coil IS. Thespinning cell can thus be operated at any desired temperature. Aplurality of conduits H are provided adjacent the bottom of the devicefor passing evaporative medium through the cell so as to evaporate thesolvent from the extruded filaments l5. The evaporative medium isremoved from the cell through outlet openings 23. The yarn comprisingthe plurality of filaments i is passed from the bottom of the spinningcell around guide roller 25 and is wound on bobbin 2 i Referring toFigure 2 of the drawing, the yarn I5 is removed from the bobbin package21 and passed about draw roller 29 and separating roller 3|. From drawroller 29, the yarn is passed to a second draw roller 33 and separatingroller 35. The yarn is passed around the two sets of draw rollersincluding their separating rollers a sufficient number of turns toprevent slippage of the yarn. Draw roller 33 is rotated at a greaterspeed, for example three to ten times the speed of draw roller 29. Inthis manner, the yarn I5 is stretched between the two draw rollers. Asthe yarn passes between the two draw rollers, a heating medium isbrought into contact with the yarn through blower nozzles 31 and 39. Theyarn passing from the draw roller 33 is wound on-bobbin 4|. The drawing.or stretching of the spun yarn as described is not claimed as part ofthe present invention, but is claimed in the copending application ofDaniel T. Meloon, Serial No. 496,397, filed July 28, 1943.

Figure 3 of the drawing illustrates a wet spinning apparatus for theproduction of yarn. The acrylonitrile polymer. solution is passedthrough conduit 5| and is extruded through spinneret 53 to form amultifilament yarn 54. The yarn 54 is passed about guide roller 51 whichis positioned Within the coagulating liquid in tank 55. The yarn is thenpassed about guide roller 59 and is wound on bobbin 6| The organicsolvent solution of polyacrylonitrile may be cast in the form of a filmas illustrated in Figure 4; In accordance with this apparatus, thepolymer solution is passed from hopper 1| on to the endless steel bandI3 where it is smoothed by means of a doctor knife 15. The band,together with the film, is passed under a means 11 for bringing a heateddrying medium into contact with the film. The film 3| is pulled from theband 13 and collected on a mill roll 83.

The polyacrylonitrile for use with the invention is preferably preparedby the ammonium persulfate catalyzed polymerization of monomericacrylonitrile dissolved or emulsified in water. It can, however, beprepared by any other suitable type of polymerization reaction such as,for example, the emulsion type reaction disclosed by U. S. Patent No.2,160,054 to Bauer et al. The

polymer preferably possesses a molecular weight within the range of15.000 to 250,000 or even higher, as calculated from viscositymeasurements by the Staudinger equation:

Molecular weight= wherein:

N,,,=specific viscosity= and I C=concentration of the solution expressedas the number of moles of the monomer (calculated) per liter ofsolution.

viscosity of solution viscosity of solvent The molecular weight of thepolymer obtained 16 pounds of acrylonitrile slowly with stirring over aperiod of two hours. The polyacrylonitrile having the above saidmolecular weight will precipitate from the solution. Increasing ordecreasing the amount of the catalyst, while maintaining the otherconditions constant, decreases or increases the molecular weight of thepolymer. Acrylonitrile copolymers and interpolymers containing at leastby weight of acrylonitrile and likewise preferably having a molecularweight of 15,000 to 250,000 or higher can be prepared in a similarmanner.

The following examples in which parts, proportions and percentages areby weight unless otherwise specified illustrate preferred methods ofpreparing solutions of polyacrylonitrile, and copolymers ofacrylonitrile in accordance with the principles of this invention and ofemploying these solutions in the manufacture of commerciallysatisfactory shaped articles of the polymer. The invention is not to belimited by the details set forth in the examples.

Example I Thirty (30) parts of an acrylonitrile polymer prepared by thepolymerization of monomeric acrylonitrile in accordance with theteachings of U. S. Patent No. 2,160,054 to Bauer et a1. and possessingan average molecular weight of 120,000 are ground to an average particlesize of 200 mesh and intimately mixed with 70 parts of p-nitrophenolground to a similar particle size. The mixture is heated over a periodof thirty minutes to a temperature of C. to form a fluid, homogeneousmass or solution which, on cooling to room temperature, forms into asolid mass that could be hot rolled or pressed into sheet form.

Example II The film is tough and much more durable and flexible at lowtemperatures (0 F.) than films prepared from similar solutions butcontaining none of the nitro-naphthol of this invention.

As above indicated, it is possible by the practice of this invention toobtain a solution of poly-.

acrylonitrile, or a copolymer or interpolymer of acrylonitrile which iseminently suited for use in the manufacture of shaped articles such asyarns, films or molded articles. These solutions are also suited for useas lacquers or coating compositions. They are especially useful in thecoating of wire and electrical parts where the high chemical andelectrical resistance of the polymer is important.

As also shown, the solvents of the invention are useful not only inconnection with the polyacrylonltrile, but also with copolymers andinterpolymers of acrylonitrile with other polymerizable substances suchas, for example, compounds containing one or more ethylenic linkagesincluding vinyl and acrylic compounds as well as olefinic or diolefinichydrocarbons such as isobutylene, butadiene, etc. They are eminentlysatisfactory for use with those polymers that contain a large amount ofacrylonitrile, for example polymers or copolymers that contain at least85% by weight of acrylonitrile and that have generally been regarded bythe art as being completely insoluble in all common organic solvents.Nor are these solvents limited to use with a p'olyacrylonitrile of anygiven molecular weight. They can be used with a polymer of almost anygiven molecular-weight and are especially satisfactory for use withthose polymers having an average molecular weight within the range15,000 to 250,000 as determined by viscosity data using the Staudingerequation and intended for use in the manufacture of yarns or films.

The solution of acrylonitrile polymer dissolved in an organic solvent inaccordance with this invention must be of such a concentration that itsviscosity at the operating temperature is within a workable range. Whenit is to be employed in the spinning of yarn or thecasting of film, thesolution should preferabl have a viscosity within the range of 25 to 750poises. When the polymer has a. molecular weight of 250,000 or more,this requires that the maximum concentration of polymer in the spinningsolution be of the order of Generally, it is preferred that the spinningsolution contain at least 10% of the polymer because of the diflicultyof rapidly removing large amounts of solvent from the solution in thespinning operation. Moreover, it is economically undesirable to use suchlarge amounts of solvent for the spinning of a given amount of polymeralthough it is true that the solvent can be completely recovered fromthe spinning operation and reused. For these reasons, it is preferred toemploy a polymer having an average molecular weight of between 40,000and 150,000 since such a polymer forms a solution of the desiredviscosity in concentrations of the order of to 25% and at a desirablespinning temperature of the order of 100 to 150 C. Of course, it iswithin the scope of the invention to heat the solution to a highertemperature, even to above the normal boiling point of thesolvent, forthe actual spinning operation. Here again, the controlling factor withregard to the temperature of the spinning solution is the viscosity ofthe solution.

The evaporative medium employed in the dry spinning of filaments andyarns or the dr casting of films in accordance with this invention maybe solution such as air, nitrogen, steam, etc, or any ning solution andthe rate of flow of the evapora- I tive medium. It is only necessarythat these several factors be so correlated that the yarn or othershaped article leaving the spinning cell besufficiently freed of thesolvent so that it is solidified and capable of being wound into packageform or otherwise collected.

Shaped articles of acrylonitrile polymer can also be formed by extrudingthe spinning solution into a suitable precipitating bath comprising aliquid that is miscible with the solvent but is a chemically inertnon-solvent for the acrylonitrile polymer. As examples of such a liquidmay be mentioned water, glycerin, organic solvents such as alcohol,ether, etc., or aqueous solutions of salts, alkalies or acids. Thecopending application of William W. Watkins, Serial No. 496,376, filedJuly 28, 1943, covers the use of glycerol and aqueous solutions of saltsas baths, preferably at elevated temperatures, for the wet spinning ofacrylonitrile polymer yarn, from solutions of the polymer, preferablywith substantial tension and stretch being applied during spinning.

The article of acrylonitrile polymer thus obtained can advantageously besubjected to a stretching operation of the type employed in the aboveexamples. This stretching is preferably performed by passing the yarnbetween two positively driven rollers, the peripheral speeds of whichare so adjusted that the article is stretched to from two to tentimesits original length, preferably approximately six times its originallength. This stretching of the formed article may be performed at anysuitable time. However,in the case of articles formed by the wetspinning or casting technique, it is preferably performed before thearticle has been completely dried. The orientation of the structure thusobtained greatly improved the physical properties of the structureincluding its tenacity, its resilience, etc.

This stretching of the shaped article can also be accomplished bycausing the article, while passing between stretching rollers, tocontact a heated stationary pin, or to pass through an inert medium suchas air, water, glycerin, etc., heated to a high temperature. Obviously,the article must not be exposed to this high temperature for a periodsufliciently long to decompose the poly mer. In general however, thetime of contact of the article with the heated medium is so short thattemperatures up to 250 C; can be employed. It is generally preferred toheat the article to a temperature of at least C. during the stretchingoperation.

In addition to acting as solvents for polyacrylonitrile, or copolymersor interpolymers of acrylonitrile, the aromatic compounds of thisinvention containing hydroxyl and nitro groups, when present in smallamounts, can also be used as plasticizing agents for the polymer, andthe higher boiling compounds of the invention are especially suited forsuch use. At the same time, it is, of course, to be understood thatnon-solvent softeners such as glycerol, etc., can also be incorporatedin the solutions of this invention, these materials remaining in-thesubsequently formed articles to impart a softening effect. If it isdesired to use such plasticizing or softening agents withpolyacrylonitrile, they are preferably-added in the desired amount to analready formed solution of the polymer in a lower boiling solvent.

This invention is primarily concerned with the steps of dissolvingpolyacrylonitrile in a suitable solvent to form a stable solutionadapted for use in the manufacture of shaped articles ofpolyacrylonitrile. It is characteristic of the invention that thesolutions provided by it are stable; the solvents do not cause adecomposition or chemical alteration oi the dissolved acrylonitrilepolymer. At the same time, it is also characteristic that the solventsprovided by the invention are also useml in the dissolving of mixturesof polyacrylonitrile and adiuvants such as dye modifiers, linearpolyamides such as nylon, derivatives 01. cellulose including celluloseethers and esters, polymers of vinyl compounds such as vinyl chloride,vinyl acetate, acrylic acid, etc., which adjuvants may be incorporatedin the acrylonitrile polymer solution to modify the properties, bothchemical and physical, oi the resulting shaped articles,

This invention provides a class of solvents for polyacrylonitrile, andcopolymers and interpolymers of acrylonitrile which were heretoforeconsidered substantially insoluble, i. e. compounds which, when liquid,will form solutions containing an appreciable amount, e. g. or more byweight of the polymer. The solvents are capable of forming with thepolymer clear solutions that are stable for extended periods of time atboth room and elevated temperatures and are admirably suited for use aslacquers or coating composi.. tions or in the manufacture of shapedarticles of the polymer, for example by extrusion into an evaporative orcoagulative medium, or by the use or a molding technique.

The invention also provides a class or materials that is eminentlysuited for use in plasticizing structures comprising the acrylonitrilepolymers. The materials provided by this invention are apparently truesolvents ior the above-mentioned acrylonitrile polymers. They do nottend to react with or decompose the polymer, the polmeric materialobtained from the solution of this invention apparently being of thesame identical chemical composition as the initial polymer,

Yarns, films and similar articles of polyacrylonitrile prepared from thesolutions of this invention can be stretched to yield orientedstructures that possess a high tenacity, a desirable elongation and ahigh elastic recovery that compares favorably with that of silk. Thearticles are not contaminated with undesirable salts and they aresubstantially tree of void spaces.

Reference, throughout the specification and claims, to acrylonitrilepolymers, polymers of acrylonitrile, and copolymers and interpolymers ofthat is. at least 85% by weight of the reactant material converted intoand forming the polymer is acrylonitrile.

Since it is obvious that many changes and modifications can be made inthe above described details without departing from the nature and spiritof the invention, it is to be understood that the invention is not to belimited to the details described herein except as set forth in theappended claims.

I claim:

1. As a new composition of matter, a polymer of acrylonitrile containingin the polymer molecule at least by weight of acrylonitrile dissolved inan aromatic compound taken from the group consisting of:

m-Nitrophenol p-Nitrophenol l-nitro-beta-naphthol 3-nitro-beta-naphthol4-nitro-beta-naphthol z-nitro-alpha-naphthol 3-nitro-alpha-naphtholi-nitro-alpha-naphthol 2. A new composition of matter as defined inclaim 1, in which said polymer is polyacrylonitrile.

3. A new composition of matter as defined in claim 1, in which saidpolymer of acrylonitrile ls non-reactive with said aromatic compound.

4. A new composition of matter as defined in claim 1, in which saidpolymer is non-reactive with said aromatic compound but is soluble inall proportions therewith.

5. A new composition of matter as defined in claim 1, in which saidpolymer has a molecular weight of between 15,000 and 250,000.

6. A new composition of matter as defined in claim 1, in which saidpolymer has a molecular weight of between 40,000 and 150,000.

'7. As a new composition of matter, a polymer of acrylonitrilecontaining in the polymer molecuie at least 85% by weight ofacrylonitrile and an aromatic compound taken from the group consistingof:

m-Nitrophenol p-Nitrophenol l-nitro-beta-naphthol s-nitro-beta-naphthol4-nitro-beta-naphthol Z-nitro-aIpha-naphthol 3-nitro-alpha-naphthol4-nitro-alpha-naphthoi 8. The composition of claim 1 in which thesolution contains at least 10% of said polymer oi acrylonitrile.

9. The composition of claim 1 in which the solution has a viscositywithin the range 25 to 750 pcises.

10. The composition of claim 1 in which the polymer is polyacrylonitrilehaving a molecular weight of between 15,000 and 250,000. l 11. Thecomposition of claim 1 in which the polymer is polyacrylonitrile havinga molecular weight of between 40,000 and 150,000.

an carom no'um.

